A 2-acyliminopyridine derivative represented by formula (I) described later is a compound useful as a pest control agent, as described in Patent Literature 5.
Methods described in Patent Literatures 1 to 5 and Non Patent Literature 2 are each known as a method for producing a pest control agent having a 2-acyl iminopyridine structure.
However, Patent Literatures 1, 2, and 3, and Non Patent Literature 2 fail to describe production in which a compound represented by formula (B) described later is used as an intermediate. Moreover, these literatures do not specifically describe the production of a compound represented by formula (I) described later. Further, Non Patent Literature 3 discloses N-(pyridin-2(1H)-ylidene]-acetamide as a tautomer of 2-acetamide pyridine, but fails to describe a specific method for producing the tautomer, or a method for producing a haloacyl derivative thereof.
On the other hand, Patent Literatures 4 and 5 disclose a specific method for producing a compound represented by formula (I). Nevertheless, although the use of an acid anhydride such as trifluoroacetic anhydride as an acylating agent generally results in a high yield in many cases because of the high reactivity, 1 equivalent of a carboxylic acid compound is by-produced. Hence, the use is industrially and economically disadvantageous and also has a great impact in the environmental aspect.
Meanwhile, the reactivity of carboxylic acid compounds is generally low, and it is difficult to use such carboxylic acid compounds for the acylation without any modification. Hence, a condensation agent is used in combination in many cases. Nevertheless, the combined use of a condensation agent brings about a problem that another waste product is generated. In other methods, an acid chloride of a carboxylic acid compound is often formed and used for the acylation. However, particularly as to trifluoroacetic acid, it is normally difficult to synthesize an acid chloride thereof unless a co-catalyst is added, as described in Non Patent Literature 4. Further, trifluoroacetyl chloride is a gas having a boiling point of −27° C., and a dedicated facility is required for the industrial use of an acid chloride derived from trifluoroacetic acid. Meanwhile, it is also possible to obtain an acylated product, as described in Patent Literature 6, by dehydrating under reflux trifluoroacetic acid together with a high-boiling-point solvent such as toluene or xylene. However, the reaction has to be carried out at a high temperature for a long period, which is industrially disadvantageous.
In sum, there has been no report so far that an acylated compound is obtained in a high yield using trifluoroacetic acid without using a condensation agent, without requiring a dedicated facility, and without needing a high-temperature, long-period reaction.